LOVE SURFACE WAVES AND ELECTRICAL RESISTIVITY USED TO DELINEATE THE NEAR SURFACE GEOPHYSICAL STRUCTURE: THEORETICAL CONSIDERATIONS

Abstract

We invert Love surface waves and electrical resistivities to cooperatively examine the physical properties of the depth range shallower than 50-m. To analyze this depth range is essential for earthquake mitigation efforts. The shear-wave velocity (VS30) is particularly important to describe the dynamic characteristics of shallow Earth. The Love surface waves are treated in terms of both phase and group velocities. The phase velocities are obtained from the slant stacking while for the group velocities the multiple filter technique is utilized. A typical shot-gather is assumed to simulate the field collection of the surface wave data. The phase velocity curve represents the average structure beneath the geophone spread. The group velocity curve represents the average structure from the source to the geophone. In a single-station fashion, for each geophone location one group velocity curve is obtained. A linear system is set up to convert these single-station group velocity curves into local group velocity curves at grid points. The latter group velocities are inverted to attain the shear-wave velocity cross section. A similar approach is adopted to study the electrical resistivity structure of the underground. We simulate the field application using a theoretical model. Multiple electrode Pole-Pole array is assumed for the field collection of the resistivity data. The apparent (measured) resistivity values are inverted to attain the true resistivity structure in terms of a cross section. The inverted structures are one-dimensional reflecting depth dependent shear-wave velocities and electrical resistivities underneath the studied region.